1. Field of the Invention
The invention relates to the field of detectors, more particularly to a detecting method and apparatus using a programmable memory device to store digitized reference values, thereby obviating the need for variable resistors to set the reference values in order to simplify the manufacture of the detecting apparatus.
2. Description of the Related Art
Indoor detecting apparatuses are commonly found in building and housing structures for safety purposes. Examples of conventional indoor detecting apparatuses include carbon monoxide detectors, fuel gas detectors such as liquefied petroleum or natural gas detectors, smoke detectors, and temperature detectors. Since a building usually has a wide variety of detecting apparatuses installed therein, whenever one of the detecting apparatuses generates an alarm signal, there is a need to inspect which one of the detecting apparatuses has detected the presence of an emergency condition before the area where the emergency condition exists can be determined. This problem arises in the prior art because the conventional detecting apparatuses are designed primarily to detect only one type of emergency condition. Aside from the resulting confusion in the event of an emergency condition, the expense that is incurred when expanding the types of emergency conditions to be detected can be astronomical.
A conventional detecting apparatus generally includes a processing unit, a sensor, a reference voltage generator, and an alarm device constituted by an alarm sound generator and a lamp indicator. FIG. 1 is a schematic circuit block diagram of a conventional carbon monoxide detector 1. As shown, a carbon monoxide sensor 11 and a reference voltage generator 12 are connected to a processing unit 10. The processing unit 10 is further connected to an alarm sound generator 13, such as a buzzer, and a lamp indicator 14, such as a light emitting diode. The reference voltage generator 12 is a variable voltage divider that includes a variable resistor VR. A variable tap of the variable resistor VR is connected to the processing unit 10 so that a reference voltage can be provided to the latter.
During the manufacture of the detector 1, there is a need to calibrate the same by adjusting the variable resistor VR so that the appropriate reference voltage can be supplied to the processing unit 10. Initially, the carbon monoxide sensor 11 is placed in a standard environment, such as a tank that contains a standard carbon monoxide concentration. Thereafter, the variable tap of the variable resistor VR is adjusted with the use of a tool, such as a screwdriver, until the processing unit 10 activates the alarm sound generator 13 and the lamp indicator 14 upon detection by the processing unit 10 that the reference voltage provided by the reference voltage generator 12 has reached the signal output of the carbon monoxide sensor 11.
In use, when the detector 1 is installed in a room of a building that is to be detected, the carbon monoxide sensor 11 generates a signal output that varies according to the carbon monoxide concentration inside the room. In the event that the signal output of the carbon monoxide sensor 11 exceeds the reference voltage from the reference voltage generator 12, indicative of an emergency condition in which the carbon monoxide concentration inside the room has exceeded the standard carbon monoxide concentration that was determined beforehand during the manufacturing stage of the detector 1, the processing unit 10 activates the alarm sound generator 13 and the lamp indicator 14 to alert the tenants of the building.
It is noted that adjustment of the variable resistor VR when calibrating the detector 1 is a time consuming task and is prone to human error.